I know of nobody who denies that the Earth has been warming for thousands of years without our help (and specifically since the Little Ice Age a few hundred years ago), and is most likely to continue to do so in its own sweet time. The important question is how much warming does the future hold, is it good or bad, and if bad is it too much for normal adaptation to handle. The real answer to the first is that no one knows, the real answer to the second is more likely good than bad (people and plants die from cold, not warmth), and the answer to the third is almost certainly not. And nobody doubts that CO2 in the atmosphere has been increasing for the better part of a century, but the disobedient temperature seems not to care very much. And nobody denies that CO2 is a greenhouse gas, along with other gases like water vapor, but despite the claims of those who are profiting by this craze, no one knows whether the temperature affects the CO2 or vice versa. The weight of the evidence [suggests] the former.
Like a lot of scientists — I’m a physicist — I assumed the “Climategate” flap would cause a minor stir but would not prompt any doubt about the threat of global warming, at least among educated, intelligent people. The evidence for anthropogenic (that is, human-caused) global warming is strong, comes from many sources, and has been subject to much scientific scrutiny. Plenty of data are freely available. The basic principles can be understood by just about anyone, and first- and second-order calculations can be performed by any physics grad student. Given these facts, questioning the occurrence of anthropogenic global warming seems crazy. (Predicting the details is much, much more complicated). [He seems to miss the point here. The usual claim is that man-made warming is large relative to other global temperature changes. That’s not predictable “by any physics grad student” and to call it a “detail” is misleading. — Seth] And yet, I have seen discussions, articles, and blog posts from smart, educated people who seem to think that anthropogenic climate change is somehow called into question by the facts that (1) some scientists really, deeply believe that global warming skeptics are wrong in their analyses and should be shut out of the scientific discussion of global warming, and (2) one scientist may have fiddled with some of the numbers in making one of his plots. This is enough to make you skeptical of the whole scientific basis of global warming? Really?
Another friend of mine used to be a math professor. He has views similar to the views of my physicist friend. “Look,” I said to him, “if you want to argue that humans are causing major global warming you should at least show it’s warmer now than in the past. Even that isn’t true. The Medieval Warm Period.” “That was only in Europe,” he replied. Actually, there is evidence of the same thing in the Gulf of Mexico.